The present invention relates generally to surgical instruments, and more particularly to providing an instrument for forming a circular opening in the lens capsule of the eye during cataract surgery.
In some people, particularly elderly people, the lens inside of the eye grows cloudy. This is referred to as a cataract. The common method of correcting this condition is to remove the natural cloudy lens and replace it with a clear synthetic lens. The natural lens is shaped like a flattened sphere, approximately 9 mm in diameter, and is contained within a capsule. The capsule is suspended radially by countless fine strings, or zonule ligaments, which are connected from the outer periphery of the capsule to the inside surface of the eyeball. In cataract surgery, an incision is made into the eye, and then a circular opening is cut into the lens capsule, typically 6 mm in diameter. (This circular opening cut into the capsule is referred to as the capsulorrhexis.) The natural lens is then broken up into smaller pieces and removed from the capsule and the eye. A synthetic lens is then put into the capsule in place of the natural lens. As this surgical procedure has improved over time, the incision size through which the instruments must pass into the eye has grown smaller and smaller. This smaller incision size contributes to a better surgical outcome due to less disturbance of the spherical shape of the clear dome section of the eye, called the cornea. At the time of this writing, the typical incision size is less than 3 mm. However, the trend is continuing towards even smaller incisions. This small incision size places greater demands for the development of better, smaller instruments.
In order to achieve an optimal surgical result, it is essential that the opening of the capsule be circular, centered, of correct diameter, and without radial tears. Ideally, the cut should be smooth and continuous. The primary techniques currently used to create this opening are the cystotome and the forceps. The cystotome is a needle with the sharp tip bent into a hook. One method of use for the cystotome is to puncture the capsule with the hook, then manipulate the tear with the hook into a generally circular shape. Another cystotome method is to create a series of punctures in a generally circular pattern, then join the punctures by tearing, creating a generally circular shape. In the method used with the forceps, a puncture is first made with a cystotome, then the torn capsule is pulled in various directions with the forceps, guiding the tearing of the capsule in a generally circular direction. Using any of these methods, even the most skilled surgeons can create unpredictable tears. Some tears deviate outward and/or inward from the intended circular path and some have jagged edges that are weak and can tear radially during the stresses put onto the capsule during the insertion of the synthetic lens. Most, if not all, are imperfect circles due to the fact that they were created by freehand movement. Tears that extend within the desired circular shape intrude into the optical zone, impairing vision. This excess material must be removed by a secondary procedure after the eye has healed from the first procedure. Tears that extend beyond the desired circular shape not only detract from a good surgical result, but they can lead to other serious complications such as a ruptured capsule or a decentered lens.
Prior devices have been developed in an attempt to create a consistent, reproducible capsulorrhexis. For example, U.S. Pat. No. 4,766,897 describes a device that mechanically directs a knife in a circular path by means of a guiding loop. The problem with this device is that the guiding loop is too large to enter into the eye through a small incision. In fact, the incision size required is equal to the diameter of the capsulorrhexis, which is not desirable. Other examples include U.S. Pat. No. 4,530,359 which describes a sharpened wire that is deflected sideways out of a tubular member, U.S. Pat. No. 5,423,841 which describes a manually controlled rotating blade, and U.S. Pat. No. 5,342,377 which describes a freely rotating blade mounted on the distal tip of a cannula. The problems associated with these types of devices are that they require the surgeon to manually move the instruments in the desired circular path, resulting not only in imperfect circles, but the motion itself produces damage to surrounding tissue, particularly the endothelium cells (located on the inside of the cornea, and once damaged, will not regenerate). Another example is U.S. Pat. No. 5,728,117 which has a circular blade constrained elliptically within a tube for entry and exit into the eye, which expands into a circle when expelled from the tube. The problems with this device are that no provision is made for the slicing action required to cut the capsule. It relies solely on penetration of a broad edge, requiring excessive downward forces onto the fragile lens capsule structure. Secondly, there are limitations as to how small it can be made, making it impractical for use in the ever-decreasing incision sizes the surgery demands. A final example is U.S. Pat. No. 5,860,994 which describes a knife mounted on a member which is rotated about a central axis, creating a circular capsulorrhexis. The problem with this device is that it has many moving parts, making it difficult to manufacture and to make it small enough to fit within the very small incisions made in modern cataract surgery. Furthermore, instruments with complex moving parts are difficult to clean and sterilize between each use due to body fluids becoming trapped in small cavities.
What is required is a smaller, simpler device, easy to learn how to use, easily cleaned and sterilized that creates smooth, continuous, properly positioned, circular capsulorrhexis cuts that are not dependent upon the accuracy of the freehand movement of the user, and can be inserted, into very small incisions.
A surgical instrument is presented which creates a circular cut of virtually any diameter in the lens capsule of the eye, yet has a diameter of less than 1 mm when inserted into the eye. A blade is attached to the distal tip of a super-elastic rod. Approximately one quarter of the super-elastic rod (the distal one quarter), is in the shape of a 360 degree loop in its relaxed position. The diameter of the loop is equal to the desired diameter of the circular cut to be made. Prior to inserting the blade into the eye, the super-elastic rod is retracted and contained within an outer tube, which is generally straight. The blade, the straightened loop constrained within the outer tube, and the outer tube are then inserted into the eye through the small incision. Once inside the eye, the loop portion of the super-elastic rod is expelled from the tube, and the super-elastic rod returns to it relaxed, 360 degree loop shape. The loop is then centered over the area where the desired circle is to be cut, and the blade is then pressed into the lens capsule, penetrating it. The superelastic rod is then retracted back into the tube. As the super-elastic rod retracts, the blade follows in a circular path, cutting the desired circular shape and diameter into the capsule. The looped section of the super-elastic rod performs the circular motion action, and the remaining section is used primarily for grip to impart motion into it, and to provide attachment to the rest of the device. Attachments can be made to the tube and the rod to facilitate handling of these small parts. The super-elastic rod is preferably made from Nitinol, an alloy of 50% nickel and 50% titanium. The cutting blade may be made from any standard knife materials, such as metal, diamond or ceramic. The outer tube can be made of any surgical grade material, such as stainless steel or plastic.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a device which the size of the cut made is controlled more by the device, and less by the freehand movement of the user;
(b) to provide a device which the shape of the cut made is controlled more by the device, and less by the freehand movement of the user;
(c) to provide a device that will allow the user to visualize the circular path and position it into the desired location prior to making the cut;
(d) to provide a device that will enable the user to create virtually any size of circular cut, yet enter the confined body space through a very small incision;
(e) to provide a device that will enable the user to easily clean and sterilize the device;
(f) to provide a device with very few moving parts, to increase the reliability of the device;
(g) to provide a device of simple design, enabling a reasonable cost of manufacture using readily available manufacturing methods;
(h) to provide a device of simple theories of operation to allow a user to quickly learn how to use it.